Reverse conducting gate turn-off thyristor

Abstract: A reverse conducting gate turn-off thyristor (RC-GTO) in which a gate turn-off thyristor (GTO) and a reverse current diode (RCD) are formed on the same substrate, includes: a gate turn-off thyristor (a); a reverse current diode (b); an anode electrode (7) provided for both the anode of the gate turn-off thyristor and the cathode of the reverse current diode; an isolation region (c) provided between the gate turn-off thyristor and the reverse current diode and having a first conducting type semiconductor layer (12) on the anode-electrode side; and second conducting type high-impurity-concentration sections (13) independently formed in the first conducting type semiconductor layer of the isolating region.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION: This invention relates to a reverse conducting gate turn-off thyristor (RC-GTO) structure in which a gate turn-off thyristor (GTO) and a reverse current diode (RCD) are formed on the same substrate. DESCRIPTION OF THE RELATED ART: A conventional reverse conducting gate turn-off thyristor will be described with reference to Fig. 6, which is a sectional view showing the essential part of a conventional reverse conducting gate turn-off thyristor. In Fig. 6, a GTO section a consists of an anode emitter layer (p E layer) 1, an anode base layer (n B layer) 2, a cathode base layer (p B layer) 3, and a cathode emitter layer (n E layer) 4. The anode base layer 2 is formed as an anode short structure due to an anode emitter short-circuiting layer (n + layer) 5 having a high impurity concentration. In Fig. 6, the RCD section b consists of an anode base layer (p B layer) 3' which is common to the cathode base layer 3 of the GTO section a , a cathode base layer (n B layer) 2' which forms a part of the same layer as the anode base layer 2 of the GTO section a , and an n + type cathode layer 6. Further, in Fig. 6, numeral 7 indicates an anode electrode provided for both the anode of the GTO section a and the cathode of the RCD section b; numeral 8 indicates a gate electrode provided on the cathode base layer 3 of the GTO section a ; numeral 9 indicates a cathode electrode provided on the cathode emitter layer 4 of the GTO section a ; and numeral 10 indicates an anode electrode provided on the anode base layer 3' of the RCD section b. The cathode electrode 9 of the GTO section a and the anode electrode 10 of the RCD section b are kept in contact with each other through a pressure contact electrode plate (not shown) arranged on the electrodes 9 and 10, so that they are at the same electrical potential. An isolation region c is provided between the GTO section a and the RCD section b. An isolation groove 11 for electrically isolating the cathode base layer 3 of the GTO section a from the anode base layer 3' of the RCD section b is provided in the isolation region c. Thus, due to the presence of the isolation groove 11, short-circuiting through the anode base layer 3' of the RCD section b, which occurs when a reverse bias voltage is applied between the gate electrode 8 and the cathode electrode 9 of the GTO section a , is prevented. Conventionally, to electrically isolate the cathode base layer 3 of the GTO section a from the anode base layer 3' of the RCD section b, the isolation groove 11 is provided with a broad width, thereby enhancing the isolation resistance (RGK) of the isolation region c. However, when the width of the isolation region 11 is provided with a broad width, the isolation region has a p-layer 12 having a broad width, so that the carrier injection efficiency of the central portion of the p-layer 12 is high, which causes the multiplication effect of the central portion of the p-layer 12 be greater than that of the GTO section a , resulting in a marked reduction in withstand voltage. As stated above, the conventional reverse conducting gate turn-off thyristor has a problem in that, when the isolation groove 11 is provideed with a broad width so as to electrically isolate the cathode base layer 3 of the GTO section a from the anode base layer 3' of the RCD section b, the multiplication effect of the central portion of the p-layer 12 of the isolation region c increases, resulting in a marked reduction in withstand voltage. Further thyristors are disclosed in DE-A-3521079, JP 53083480, JP 56104467 and CH594989. SUMMARY OF THE INVENTION This invention has been made with a view toward solving the above problem. It is an object of this invention to provide a reverse conducting gate turn-off thyristor which makes it possible to obtain high withstand voltage while providing the isolation region with a broad width. According to the present invention as claimed in claim 1, there is provided a reverse conducting gate turn-off thyristor comprising: a gate turn-off thyristor; a reverse current diode; an anode electrode provided for both the anode of the gate turn-off thyristor and the cathode of the reverse current diode; an isolation region provided between the gate turn-off thyristor and the reverse current diode and having a first conducting type semiconductor layer on the anode-electrode side; and second conducting type high-impurity-concentration sections independently formed in the first conducting type semiconductor layer of the isolating region. BRIEF DESCRIPTION OF THE DRAWINGS Figs. 1A and 1B are a sectional view and a plan view, respectively, showing the essential part of a reverse conducting gate turn-off thyristor according to a first embodiment of this invention; Fig. 2 is a plan view showing the overall construction of the first embodiment; Fig. 3 is a diagram showing the relationship between the withstand voltage V DRM with respect to the width of the p-layer of the isolation region c and the value of dV/dt at the time of commutation failure; Fig. 4 is a sectional view showing the essential part of a modification of the first embodiment; Figs. 5A and 5B are a sectional view and a plan view, respectively, showing the essential part of a reverse conducting gate turn-off thyristor according to a second embodiment of this invention; and Fig. 6 is a sectional view showing the essential part of a conventional reverse conducting gate turn-off thyristor. DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment: The first embodiment of this invention will be described with reference to Figs. 1A and 1B, which are a sectional view and a plan view, respectively, showing the essential part of a reverse conducting gate turn-off thyristor according to a first embodiment of this invention. Those components which correspond to those of the conventional example shown in Fig. 6 will be indicated by the same reference numerals, and a detailed description of such components will be omitted. This embodiment differs from the conventional example in that high-impurity-concentration n + sections 13, serving as a high-concentration impurity layer, are arranged at equal intervals in the p-layer 12 in the lower section of the isolation region c, which isolates the gate turn-off thyristor (GTO section a ) from the reverse current diode (RCD section b). As shown in Fig. 2, the GTO section a is formed as an annular zone arranged around the RCD section b, which has a circular configuration, through the intermediation of the isolation region c. The RCD section b, the isolation region c and the GTO section a are formed concentrically, and the high-concentration n + sections 13, shown in Figs. 1A and 1B, are formed as a plurality of concentrical rings sharing the same center with the above-mentioned concentric components and arranged at equal intervals. In the isolation region c, which has a width of 3.9 mm, the n + sections 13. each having a width of approximately 100 µm, are formed at a pitch of 400 µm. The n + sections 13, which are formed by diffusion simultaneously with the n + layer 5 in the GTO section a , have a surface impurity concentration of 1.5 × 10 21 cm -8 and a depth of 30 µm as measured from the anode electrode 7. The p-layer 12 of the isolation region c is divided into a plurality of parts by the n + sections 13. Each part has a width of approximately 300 µm, which is approximately 1.7 times as broad as the width of each section of the p E layer 1 in the GTO section a , which is 180 µm. The p-layer 12 of the isolation region c and the p E layer 1 of the GTO section a have a depth of 25 µm as measured from the anode electrode 7. In the reverse conducting gate turn-off thyristor of the first embodiment, a plurality of n + sections 13 are arranged at equal intervals in the p-layer 12 of the isolation region c, so that the width of each of the plurality of parts of the p-layer 12 in the isolation region c, defined through division by the n + sections 13, can be much narrower than the width of the p-layer in the conventional example. Therefore, the central portion of the p-layer 12 is little subject to carrier multiplication, so that a reduction in withstand voltage does not occur even if a high voltage is applied. In an experiment, satisfactory results could be obtained by providing each part of the p-layer 12 with approximately the same width as that of each section of the anode emitter layer (p E layer) in the GTO section a . For example, in a 2000A class reverse conducting gate turn-off thyristor having a similar construction to that shown in Figs. 1A and 1B, the width of each part of the p-layer 12 of the isolation region c was varied in the range of from 100 to 2000 µm while maintaining the same width of 200 µm for each section of the p z layer 1 of the GTO section a . In this condition, the relationship between the withstand voltage V DRM with respect to the width of the p-layer 12 of the isolation region c and the value of dV/dt at the time of commutation failure was examined, and the results as shown in Fig. 3 were obtained. The results show that the optimum width of each part of the p-layer 12 is in the range of 200 to 1000 µm, within which both the withstand voltage V DRM and the value of dV/dt are not less than design values of S and T, respectively. Further, conventionally, formation of n-type sections in the p-layer 12 of the isolation region c would result in surplus carriers being injected into the cathode emitter layer (n E layer) 4 of the GTO section a at the time of reverse recovery of the diode, thereby causing a break-through. In the first embodiment, however, there is no fear of such a problem since the area of n + sections 13 is very small. As stated above, it is an object of the first embodiment of this invention to improve the withstand voltage of a reverse conducting gate turn-off thyristor without involving an increase in the number of processes or deteriorating the other characteristics of the thyristor. For this purpose, ring-like high-impurity-concentration n + sections 13 are formed at equal intervals in the p-layer 12 of the isolation region c, which is between the gate turn-off thyristor and the reverse current diode. Generally speaking, in a semiconductor device, the depletion layer greatly expands toward the n B layer when a reverse bias voltage is applied. This depletion layer expands to the proximity of the p E layer on the anode side and to the proximity of the p-layer in the isolation region, with the result that carrier multiplication is liable to occur. In the first embodiment of the present invention, however, the high-impurity-concentration n + sections 13 are arranged in a split form in the p-layer of the isolation region, thereby restraining carrier multiplication and making it possible to obtain high withstand voltage characteristics. When, as shown in Fig. 4, the depth of the p-layer 12 in the isolation region c as measured from the anode electrode 7 is smaller than the depth of the p E layer 1 in the GTO section a , it is possible to more effectively restrain carrier multiplication and obtain still higher withstand voltage characteristics. Second Embodiment: While in the first embodiment a plurality of ring-like n + sections 13, each having a width of 100 µm, are formed at a pitch of 400 µm in the isolation region c, having a width of 3.9 mm, it is also possible, as shown in Figs. 5A and 5B, to provide a plurality of dot-like n + sections 12 in the p-layer 12 of the isolation region c. The n + sections 13, each having a diameter of 100 µm, are arranged at intervals of 400 µm. The impurity concentration and diffusion depth of the n + sections 13 in this embodiment are the same as those of the n + sections 13 in the first embodiment. The withstand voltage of the reverse conducting gate turn-off thyristor of this invention is determined by the width of the p-layer 12 of the isolation region c. However, the value of dV/dt at the time of commutation failure depends upon the area of the n + sections 13 in the isolation region c. In the second embodiment, the n + sections 13 in the isolation region c are formed in a dot-like fashion, so that the area of the n + sections 13 can be reduced to approximately 0.03 to 1 % as compared with that of the n + sections 13 in the first embodiment, whereby it is possible to heighten the value of dV/dt at the time of commutation failure. Although in the first and second embodiments the GTO section a in the form of a ring-like zone is formed around the round RCD section b, as shown in Fig. 2, this should not be construed restrictively. It is also possible to arrange a ring-like RCD section b around a round GTO section a . A reverse conducting gate turn-off thyristor (RC-GTO) in which a gate turn-off thyristor (GTO) and a reverse current diode (RCD) are formed on the same substrate, includes: a gate turn-off thyristor; a reverse current diode; an anode electrode provided for both the anode of the gate turn-off thyristor and the cathode of the reverse current diode; an isolation region provided between the gate turn-off thyristor and the reverse current diode and having a first conducting type semiconductor layer on the anode-electrode side; and second conducting type high-impurity-concentration sections independently formed in the first conducting type semiconductor layer of the isolating region.

Claims: A reverse conducting gate turn-off thyristor comprising: a gate turn-off thyristor ( a ); a reverse current diode ( b ); a common electrode ( 7 ) provided for both an anode of said gate turn-off thyristor section and a cathode of said diode section ( b ); an isolation region ( c ) provided between said gate turn-off thyristor and said diode ( b ) and having a first conducting type semiconductor layer ( 12 ) on the side of said electrode ( 7 ); said gate turn-off thyristor ( a ), said diode ( b ) and said isolation region ( c ) having a common first conducting type layer ( 3, 3 ') and a common second conducting type layer ( 2 , 2 '); wherein said gate turn-off thyristor ( a ) includes a second conducting type high impurity concentration layer ( 5 ) and a plurality of first conducting type anode emitter regions ( 1 ) arranged in said second conducting type high impurity concentration layer ( 5 ) such that both said conducting type high impurity concentration layer ( 5 ) and said anode emitter regions ( 1 ) are in contact with said common second conducting type layer ( 2, 2 ') and said electrode ( 7 ), each anode emitter region ( 1 ) having a width; characterized in that a plurality of second conduction type high-impurity-concentration regions ( 13 ) are arranged in said first conducting type semiconductor layer ( 12 ) of the isolation region ( c ) such that both said first conducting type semiconductor layer ( 12 ) and second conduction type high-impurity-concentration regions ( 13 ) are in contact with said common second conducting type layer ( 2, 2' ) and said electrode ( 7 ), and said second conduction type high-impurity-concentration regions ( 13 ) are spaced apart from each other by a distance approximately equal to the width of said anode emitter regions ( 1 ) of said gate turn-off thyristor ( a ). A thyristor according to Claim 1, characterized in that said gate turn-off thyristor ( a ), said reverse current diode ( b ) and said isolation region ( c ) are formed concentrically with respect to each other. A thyristor according to Claim 2, characterized in that said high-purity-concentration regions ( 13 ) are formed as a plurality of ring-like sections arranged at equal intervals and sharing the same center with said gate turn-off thyristor ( a ), said reverse current diode ( b ) and said isolation region ( c ). A thyristor according to Claim 1, characterized in that the first conducting type semiconductor layer ( 12 ) of said isolation region ( c ) has a depth as measured from said electrode side which is smaller than that of the anode emitter region ( 1 ) of said gate turn-off thyristor ( a ). A thyristor according to Claim 2, characterized in that said high-impurity-concentration regions ( 13 ) are formed as a plurality of dot-like sections arranged at equal intervals. A thyristor according to Claim 1, characterized in that the first conducting type semiconductor layer ( 12 ) of said isolation region ( c ) is a p-type layer while the second conducting type high-impurity-concentration regions ( 13 ) are n + sections. A thyristor according to any of the Claims 1 to 6, characterized in that said distance between said second conduction type high-impurity-concentration regions ( 13 ) is in a range from 200 µm to 1000 µm.

Inventors: MORISHITA KAZUHIRO, TOKUNOH FUTOSHI, MORISHITA, KAZUHIRO, TOKUNOH, FUTOSHI, MORISHITA, KAZUHIRO, C/O FUKURYO SEMICON ENG.CORP., TOKUNOH, FUTOSHI, C/O MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1994
Main classification: H01L29
IPC codes: H01L29